E-Mail IMAGE: Using an experimental technique whereby flowers can be coaxed to form from plant roots, biologists led by the University of Pennsylvania's Doris Wagner uncovered a protein that enables for the... view more Credit: University of Pennsylvania Cells don't express all the genes they contain all the time. The portion of our genome that encodes eye color, for example, doesn't need to be turned on in liver cells. In plants, genes encoding the structure of a flower can be turned off in cells that will form a leaf. These unneeded genes are kept from becoming active by being stowed in dense chromatin, a tightly packed bundle of genetic material laced with proteins.